Lightweight Electric/Hybrid Vehicle Design

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142 Lightweight Electric/Hybrid Vehicle Design type of drive that would be used on trucks between 150 kW and 1000 kW. In pollution and fuel economy terms, hybrid technology should be able to deliver two-thirds fuel consumption and one-third noxious emission levels of IC engined vehicles. This technology would just about maintain the overall emissions status quo in 10 years overall. If hybrid vehicles were used on battery only in cities, this would have a major impact on local pollution levels. (a) (c) (d) Fuel consumption (1/100 km) 9 8 7 6 5 4 3 2 1 0 -10 -5 0 5 10 15 20 SOC balanced with an assumed battery Electric energy consumption (kWh/100 km) ‘Independent hybrid’ ‘Substitution hybrid’ Days Number in % Speed (km/h) 30 20 10 0 60 50 40 30 20 10 0 20 40 60 80 200 250 200 Last Daily Distance travelled (km) Daily distances SOC balanced with an ideal lossless battery Athens Germany UK France All Trip Number in % 18% 20% Fig. 6.2 HYZEM research programme: (a) characterizing a hybrid powertrain; (b) use of vehicle per day; (c) daily distances and trip lengths; (d) synthetic urban drive cycle. 32% (b) Trip length distribution More None 5 - 8 Athens Germany UK France All 1 2 3 4 5 6 7 8 9 10 15 20 30 50 100 >100 Trip length distribution 0 0 100 200 300 Time (s) 400 500 1 to 4 30%
6.2 Hybrid-drive prospects Hybrid vehicle design 143 A neat description of the problems of hybrid-drive vehicles has come out of the results of the 3 year HYZEM research programme undertaken by European manufacturers, Fig. 6.2. According to Rover participants 1 , controlled comparisons of different hybrid-drive configurations, using verified simulation tools, are able to highlight the profitable fields of development needed to arrive at a fully competitive hybrid-drive vehicle and demonstrate, in quantitative terms, the tradeoff between emissions, electrical energy and fuel consumption. Only two standard test points are required to describe the almost linear relationship: fuel consumption at point of no overall change in battery state-of-charge (SOC) and point of electrical consumption over the same cycle in pure electric mode. A linear characteristic representing an ideal lossless battery can also be added to the graph, to show the potential for battery development, as at (a). Confirmation was also given to such empirical assessments that parallel hybrids give particularly good fuel economy because of the inherent efficiency of transferring energy direct to the wheels as against the series hybrids’ relatively inefficient energy conversion from mechanical to electrical drive. The need for a battery which can cope with much more frequent charge/discharge cycles than one for a pure electric-drive vehicle was also confirmed. Although electric energy capability requirement is less stringent, a need to reduce weight is paramount in overcoming the problem of the redundant drive in hybrid designs. A useful analysis of over 10 000 car journeys throughout Europe was undertaken for a better understanding of ‘mission profile’ for the driving cycles involved. Cars were found to be used typically between one and eight times per day, as at (b), and total daily distances travelled were mostly less than 55 km. Some 13% of trips, (c), were less than 500 metres, showing that we are in danger of becoming like the Americans who drive even to visit their next door neighbours! Even more useful velocity and acceleration profiles were obtained, by data recoding at 1 Hz frequency, so that valuable synthetic drive cycles were obtained such as the urban driving one shown at (d). 6.2.1 MAP-CONTROLLED DRIVE MANAGEMENT BMW researchers 2 have shown the possibility of challenging the fuel consumption levels of conventional cars with parallel hybrid levels, by using map-controlled drive management, Fig. 6.3. The two-shaft system used by the company, seen at (a), uses a rod-shaped asynchronous motor, by Siemens, fitted parallel to the crankshaft beneath the intake manifold of the 4-cylinder engine, driving the tooth-belt drive system as seen at (b); overall specification compared with the 518i production car from which it is derived is shown at (c). The vehicle still has top speed of 180 kph (100 kph in electric mode) and a range of 500 km; relative performance of the battery options is shown at (d). Electric servo pumps for steering and braking systems are specified for the hybrid vehicle and a cooling system for the electric motor is incorporated. The motor is energized by the battery via a 13.8 V/50 A DC/DC converter. The key electronic control unit links with the main systems of the vehicle as seen at (e). To implement the driving modes of either hybrid, electric or IC engine the operating strategy is broken down into tasks processed parallel to one another by the CPU, to control and monitor engine, motor, battery and electric clutch. The mode task determines which traction condition is appropriate, balancing the inputs from the power sources; the performance/output task controls power flow within the total system; the battery task controls battery charging. According to accelerator/braking pedal inputs, the monitoring unit transfers the power target required by the driver to the CPU where the optimal operating point for both drive units is calculated in a continuous, iterative process. The graphs at (f) give an example of three iterations for charge efficiency, also determined by the CPU, based on current charge level of the battery.
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viii Preface natural gas, which is
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Page 131 and 132: PART TWO Battery/fuel-cell EV desig
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Page 141 and 142: Battery/fuel-cell EV design package
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Page 169: 6.1 Introduction 6 Hybrid vehicle d
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Page 177 and 178: M [Nm] 500 450 400 350 300 250 200
Page 179 and 180: 6.3.6 TAXI HYBRID DRIVE Hybrid vehi
Page 181 and 182: Hybrid vehicle design 153 The Rover
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Page 189 and 190: Hybrid vehicle design 161 power and
Page 191 and 192: Hybrid vehicle design 163 The batte
Page 193 and 194: Hybrid vehicle design 165 into mech
Page 195 and 196: Hybrid vehicle design 167 drive ele
Page 197 and 198: Hybrid vehicle design 169 The view
Page 199 and 200: Hybrid vehicle design 171 6.5.4 ADV
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(a) M b Mb Mt 3 2 1 T (b) (c) t s T
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252 Lightweight Electric/Hybrid Veh
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Lightweight Electric/Hybrid Vehicle Design

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